The GPLA complex is the major histocompatibility complex of the guinea pig. It contains genes regulating several aspects of the immune response, as well as genes determining the GPLA-B and S histocompatibility antigens and Ia antigens. The research proposed utilizes a chemical approach to determine how the structure of the GPLA-B/S and Ia antigens influences their function. Detergent-solubilized, radiolabeled, partially purified antigen-bearing molecules will be isolated by immune precipitation, and where appropriate, separated into their component chains. These chains will then be characterized by isoelectric focusing, and tryptic and cyanogen bromide peptide mapping. Partial N-terminal amino acid sequencing will be done using the microsequencing technique. The protein versus carbohydrate nature of the antigenic determinant will be explored using a glycosylation inhibitor, tunicamycin. Relationships between the antigen molecules on the cell membrane will be examined using reversible cross-linking reagents. T cell receptors for antigens will be chemically characterized by the same techniques.